The presence of microbial contamination in clinical specimens is conventionally determined by culturing the specimens in the presence of nutrients and detecting microbial activity through changes in the specimen or in the atmosphere over the specimen after a period of time. For example, in U.S. Pat. No. 4,182,656 to Ahnell et al., the sample is placed in a container with a culture medium comprising a carbon 13 labeled fermentable substrate. After sealing the container and subjecting the specimen to conditions conducive to biological activity, the ratio of carbon 13 to carbon 12 in the gaseous atmosphere over the specimen is determined and compared with the initial ratio. In U.S. Pat. No. 4,152,213, a method is claimed by which the presence of oxygen consuming bacteria in a specimen is determined in a sealed container by detecting a reduction in the amount of oxygen in the atmosphere over the specimen through monitoring the pressure of gas in the container. U.S. Pat. No. 4,073,691 provides a method for determining the presence of biologically active agents, including bacteria, in a sealed container containing a culture medium by measuring changes in the character if the gaseous atmosphere over the specimen after a period of time.
A method for non-invasive detection is taught by Calandra et al., U.S. Pat. No. 5,094,955, where a device is disclosed for detecting the presence of microorganisms in clinical specimens, such as blood or other body fluids, and in non-clinical specimens, by culturing the specimens with a sterile liquid growth medium in a transparent sealed container. The presence of microorganisms is determined by detecting or measuring changes in the pH of the specimen or the production of carbon dioxide within the specimen using a sensor affixed to the interior surface of the container or to the sealing means used to seal the container. In Calandra et al., microorganisms can be detected in the presence of interfering material, such as large concentrations of red blood cells, through non-radiometric and non-invasive means.
One disadvantage of the detection system of Calandra et al. is that the time required for detecting the presence of microorganisms is related to the number or microorganisms within the sample. Also, because the growth medium for the microorganisms is a liquid, the container must usually be agitated during incubation, which is an additional expense involved in making the incubation equipment, as well as an increase in the likelihood of a mechanical breakdown. Also, such a system allows for the determination of the presence of microorganisms, but does not allow for enumeration. Furthermore, it is often the case that after detection of microorganisms, it is desired to identify the microorganisms and/or determine their susceptibility to various antibiotics. In a Calandra-type system, it would be necessary to plate out the microorganisms from the liquid culture medium before performing susceptibility or identification tests, which involves additional timexe2x80x94time that is not always available if the patient is very ill.
The present invention relates to a device and method for detecting the presence of microorganisms in clinical and non-clinical specimens. The device, hereinafter referred to as the xe2x80x9csensor platexe2x80x9d, provides an environment to culture microbial organism colonies from a liquid sample, and a means to facilitate microbial detection and quantification, either manually or with an instrument. The sensor plate comprises a solid, semi-solid or powdered gel immobilization matrix layer and a sensor layer. Detected microbial colonies are isolated and immediately available for further testing.
More particularly, the sensor plate provides an area for accepting an unknown liquid sample (unknown whether microorganisms are present or not) a mechanism to immobilize the liquid sample on an interior surface of the plate, components (e.g. nutrients) to facilitate growth of microorganisms in the sample, and a sensor for allowing the detection and enumeration of microorganism colonies within the sample. The sensor plate can be comprised of an immobilization layer (e.g. a gel layer) and a sensor layer, with a sample being absorbed into, or forming a gel with, the immobilization matrix layer. A sensor layer can be located on at least one surface of the sensor plate to indicate the presence of microorganisms. Small areas or zones of color changes occur in the sensor layer which indicate actual microorganism colony growth in the immobilization layer. The sensor plate is inspected manually or automatically with an instrument to determine the presence, location and/or number of microorganism colonies.
Various other features and advantages of the invention will become apparent from the detailed description below taken in conjunction with the accompanying drawings and the appended claims.